Prior to the present invention, a device having a stop for a plate valve used in an air compressor has been taught in the prior art. See, for example, German Pat. No. DE-AS 1 129 784, wherein plate valves, which are in the form of valve plates, which are fastened on one side thereof, are used in the opening and closing of the valve passages of an air compressor. In this prior art, in each case, the free end of each of the valve plates is moved against a stop.
The stop is located on various components such as the cylinder, the cylinder head, or a valve support. Due to the conventional manufacturing procedures that are used, these components of a pneumatic compressor usually consist of a castable material. Such castable material generally being either aluminum or gray cast iron. The problem is that the resistance of these materials against surface wear is relatively less than the wear resistance of the spring steel which is conventionally used in manufacturing a valve plate.
Furthermore, due to these different properties of the material used in manufacturing such valve plate and stop, the surface of the stop is subjected to added wear which in turn can lead to a detrimental deformation of such stop in a relatively short period of time, thereby causing added maintenance on such compressor. The added wear is primarily the result of an impact effect that is exerted by the valve plate on the stop in conjunction with a surface friction which occurs between the stop and the valve plate. Such surface friction between the stop and the valve plate occurs due to the fact that the elastic free end of the spring steel valve plate will bend when such valve plate hits the stop.
Additionally, the increase of the lift of the valve plate brought about by the surface erosion of the stop has the inherent disadvantage that the impact effect will gradually be increased. This gradual increase in the impact effect is due to the extension of the oscillation of such valve plate. Furthermore, the friction created between the stop and the valve plate increases simultaneously. This would be expected because the extending oscillation of the valve plate is associated with a more pronounced bending effect in the free end of the valve plate. All this means that the factors determining the wear, i.e., impact and friction, intensify in a disadvantageous manner with increasing wear and that, for this reason, such wear becomes progressively worse.
As would be expected by persons skilled in the pneumatic compressor art, an additional disadvantage of the increasing amount of lift of such valve plate lies in the delayed closure time of the valve openings, thereby decreasing the efficiency of such compressor.
For example, the delayed closure of the upstroke valve opening will result in a decrease of the output of the compressor. The reason for such reduced output of the compressor is that a portion of the air which was taken in can be recirculated into the suction portion of the compressor at the beginning of each compression stroke.
Aside from an unwanted impairment of the output of such compressor, the delayed closure of the pressure valve opening can also cause a detrimental increase in the thermal strain on the compressor since an already compressed, i.e., heated, pressurized air is permitted to flow back from the pressure area to the compression space at the beginning of each intake stroke of such pneumatic compressor.
Also noteworthy as one of the several problems associated with prior art stops is the increase of the lift of such valve plate. Such lift problem is caused by the surface wear of the stop and has the additional disadvantage that the risk of rupture at the root of the valve plate is enhanced.
It is conceivable to improve the resistance against wear of the stop surface through the use of appropriate tempering on surface hardening metallurgical techniques. Even though techniques of this kind would only have to be utilized in the area of the stop and not over the entire surface area of the component, including such stop, they would, however, require rather expensive manufacturing procedures, such as case hardening. Application of these techniques, therefore, would not be a cost-effective solution to the problem in a volume production arrangement of such components.